Traditional gaming terminals or slot machines have a plurality mechanical reels, which rotate and then stop to show symbols on one or more paylines drawn across the reels. Players wager coins or credits on one or more of these paylines and are paid for certain combinations of symbols randomly displayed on a payline for which a wager has been placed. Video slot machines typically show the same type of reel configuration but only on a video display. Some slot machines award “scatter” pays when a specific symbol(s) appears in any visible position (not necessarily on the payline) on certain reels. One concept that has been successfully employed to enhance the entertainment value of a game is that of a “secondary” or “bonus” game which may be played in conjunction with a “basic” game. The bonus game may comprise any type of game, either similar to or completely different from the basic game, and is activated on the occurrence of a selected event or outcome of the basic game. Such a bonus game produces a significantly higher level of player excitement than the basic game because it provides a greater expectation of winning than the basic game alone.
Another concept that has been employed in wagering games to add player excitement is a symbol shifting feature. For example, some slot machines use a “nudge” feature (e.g. “Double Diamond Deluxe” by IGT) after the results of the game are displayed. Such a feature allows certain symbols to rise to the payline when they appear below the payline, or other symbols will fall to the payline when they appear above the payline. Similarly, some games allow the player to “nudge” certain symbols after the result of the game is displayed in an to attempt to modify the original result and achieve a better result
Another wagering game using a symbol shifting feature is disclosed in U.S. Patent Publication No. 2004/0033829 entitled Symbol Matching Gaming Machine, which is commonly owned by the assignee of the present application. In one embodiment, a screen displays a matrix of randomly generated game symbols, which are from a predefined set of symbols. In order to receive credits, a winning combination of symbols must exist. Winning symbol combinations are created by interchanging the positions of symbols. When a winning combination of symbols is formed, the player is awarded credits, the winning combination symbols are removed, and all of the symbols above the removed symbols cascade down to fill in the empty spaces. The empty spaces created by the removal of symbols forming a winning combination are filled by adding additional randomly generated symbols.
Still yet another game utilizing a symbol shifting feature is described in U.S. Patent Publication No. 2004/0043809 entitled “Chain Reaction Game” and is commonly owned by the assignee of the present application. In one embodiment, a screen displays a matrix of randomly generated game symbols. Once displayed, the symbols are analyzed to determine if any winning combinations of symbols exist. If a winning combination(s) exists, the player is awarded the number of credits corresponding to the combination, and the winning combination of symbols is removed. Once the winning combination is removed, the symbols in the column above each symbol forming a part of the winning combination move down to fill in the empty spaces in the matrix. The symbols are again analyzed to determine if any winning combinations exist. In no winning combination exists, the game is over. If a winning combination exists, the game continues as previously discussed until no further winning combinations are created at which time the game is over.
Due to player appeal, gaming terminals having shifting symbol features are common. Accordingly, in the competitive gaming machine industry, there is a continuing need for gaming machine manufacturers to produce new types of games, or improvements to existing games using shifting symbol features, which will attract frequent play by enhancing the entertainment value and excitement associated with the game. Preferably, such new features will maintain, or even further enhance, the level of player excitement. The present invention is directed to satisfying these needs.